Low carbon high tensile strength alloy steel

ABSTRACT

A LOW CARBON, WELDABLE HIGH RENSILE STRENGTH ALLOY STEEL CHARACTERIZED BY DUCTILITY AND TOUGHNESS SUITABLE FOR STRUCTURAL USES IS PRODUCED IN THE &#34;AS ROLLED&#34; CONDITION BY UTILIZING A STEEL CONSISTING, ESSENTIALLY, BY WEIGHT, OF   PERCENT, ABOUT CARBON .10-.20 MAGANESE .75-1.15 SILICON .50-1.0 CHROMIUM .50-.80 ZIRCONIUM .05-.20 BORON .0005-.0025 TITANIUM .02-.15 COLUMBIUM .01-.06   AND THE BALANCE IRON WITH RESIDUAL IMPURITIES. THE STEEL IS HOT ROLLED TO FORM BARS, PLATE AND SHEETS WITH A STARTING ROLLING TEMPERATURE BETWEEN 2100*F.-2300*F. AND A FINISHING ROLLING TEMPERATURE BETWEEN 1400*F.-1700*F. FOLLOWED BY AIR COOLING.

United States Patent Int. Cl. C22c 39/14 US. Cl. 75-126 F 3 Claims ABSTRACT OF THE DISCLOSURE A low carbon, weldable, high tensile strength alloy steel characterized by ductility and toughness suitable for structural uses is produced in the as rolled condition by utilizing a steel consisting essentially, by weight, of

Percent, about and the balance iron with residual impurities. The steel is hot rolled to form bars, plate and sheets with a starting rolling temperature between 2l00 F.2300 F. and a fiinishing rolling temperature between 1400 'F.-1700 F. followed by air cooling.

This invention is a division of copending application Ser. No. 659,885, filed Aug. 11, 1967, which is concerned with low carbon, high tensile strength, alloy steel. More specificially it is concerned with low carbon, high tensile strength, alloy steel having a minimum tensile strength of about 75,000 p.s.i. in the as rolled condition.

Low carbon, high tensile strength steels of the prior art have required heating, quenching, and tempering treatments subsequent to rolling in order to develop the desired tensile strengths and suitable ductility and toughness. Such treatments require multiple and uneconomical handlings e.g. the product must be held rigidly to prevent warping while being cooled rapidly from a temperature about 1750 R, and higher, to room temperature in about to 25 seconds.

The quenching develops 100% marstenitic steel and is required to obtain desired high tensile strength. Without such quench treatment, such steels have a tensile strength of about 50,000 to 60,000 p.s.i. in the as rolled condition.

After quenching, such steels previously required a tempering treatment at about 850 F. to about 1300 to develop ductility and other properties necessary for end product usage.

This invention provides an alloy steel with high tensile strengths in the range of about 80,000 to about 120,000 p.s.i. (minimum yield strength of 75,000 p.s.i.). In addition, the steel exhibits ductility and yield point elongation values suitable for normal fabrication of high tensile strength steels and toughness suitable to withstanding normal stresses encountered in use of such steels. Obtaining these results without treatment subsequent to rolling is one of the highly unexpected contributions of the invention.

The low carbon high tensile strength alloy steel of the present invention consists essentially of the following weight-percentages:

Patented Sept. 5, 1972 the balance being iron with residual impurities such as are ordinarily encountered in conventional basic oxygen, open hearth, or electric furnace practice used in producing the steel. The maximum desirable values of the most common residual impurities encountered are:

- Max. Phosphorus .04 Sulphur .05 Copper .35 Alumium .07

The upper limit of carbon is ordinarily not exceeded in order to maintain the good weldability of end product provided by the invention. Carbon content below the lower limit is ordinarily avoided in order to have sufiicient carbon available for providing desired tensile strength.

The manganese is added in the furnace or the ladle. Where possible, e.g. in open hearth practice, it is added in both the furnace and the ladle. Preferably, the manganese is maintained in the range of .85 to 1.0% with a specific value of 30% being desired. The manganese helps increase the yield point and tensile strength of the steel and aids cold formability.

Silicon acts as a deoxidizer and ferrite strengthener. It can be added in the furnace or ladle; where possible silicon is added in both. Silicon is desirably kept in the range of .75% to .90% with .85 being preferred.

The chromium is added in the ladle and acts to increase both the yield point and tensile strength of the steel. A preferred'specific value for the chromium is .65%.

The zirconium acts to increase hardenability, refine grain structure, increase toughness and cold formability. It is added in the ladle and is preferably kept between .075 and .12%; with .08% being the specific value aimed for.

The boron is added in the ladle. It increases hardenability of the steel and seeks out remnants of nitrogen in the steel to a greater extent than other nitride formers such as chromium, zirconium, columbium. The titanium helps to protect the boron for this purpose because of its greater aflinity for oxygen than boron. A preferred value for the boron is .0010% and a preferred range is .0005% to .012%. The titanium also acts as a carbide former and is preferably kept at about .03%. The titanium should be added with the boron.

Columbium contributes to a number of the unexpected results obtained through the invention. It raises the yield point significantly without detrimental effect on the highly desirable ductility and toughness obtained by the invention in the as rolled condition. The columbium is added in the ladle, or can be added in the mold. A preferred specific value for the columbium is .035 and the preferred range is .035 to .06%.

If the steel is degassed during processing the ladle additions are made after degassing to minimize oxidation products and reduce possible contamination of the steel.

The alloy steel of this invention is rolled into bars, plate or sheets which are suitable for structural uses, railway car framing, and the like. This steel is characterized by high tensile strength, good weldability, high energy absorption capacity, and good ductility and yield point elongation values in the as rolled condition. Data on these properties are set forth in the representative examples below:

4 v able form for rolling into bars, plates or sheets. The billets are heat soaked at about 2100 to 2300 F., preferably about 2150 F., prior to rolling. The billets are then rolled. Multiple stand rolling is carried out so that finish- 5 ing rolling temperature of the product of the present in- %ggggi g X fi}gfi T %E vention can be about 200 to 300 lower than the finishing STRENGTH OF 75,000 .s.i. rolllng temperatures employed with high tcnslle strength g fgtwfg u steels in the prior art. The finishing rolling temperature 4 5"); .3121: 110" should be in the range of 1400 to about 1700 F.

10 After rolling the product is allowed to cool without Mn P s- 'si Cr Zr 13 Ti Ob quenching or forced cooling. Such cooling will ordinarily Ladle take place at a rate of about to per second at least chemistry .17 .04 .013 .010 .00 .74 .08 .0012 .03 .038 through the major portion of the cooling depending on the Reeheck I chemistry shape and thickness of the final product. I an e 75 W14 10 h r advantages of the invention are inherent m the .312 .17 .97 .ss .70 .10 .0014 .03 .037 above s lptl n. It IS underst od that changes and modifications in the foregoing teachings can be made Without departing from the spirit of the invention so that the scope MECHANICAL PROPERTIES of the invention is to be determined from the appended Elongation, 2O clams" Ys '1 S percent B I claim: Bars Inches end 1. A low carbon, 75,000 p.s.i. minimum yield strength 2" Offset H-giuches alloy steel consisting essentially, by weight, of 8.11

Fro tu 29-21-15 SB. x T Middle. 29-21-10 SB & x 'r 25 Back- 241611 SB... x '1 .312 gauge:

103, 700 7- 4 Back 105, 0 30-22-10 s13 Percent, about Carbon .07-.20, 30 Manganese .75-l.15 Silicon .50-1.0 K I CHARPY V IMPACT TEOST DATA Chromlum 50 .80 [Ft.-lbs.atten1pe1ature F.] Zirconium 05120 Room Boron .0005-.0025

30 Titanium about .15% max.

pera- Thickness Direction ture s2 0 -20 -40 Columbmm 01 .250 Transverse 12.7 9.0 6.7 4.8 3.0 2.2 Longitudinal 24.3 17.7 13.8 13.3 0.0 4.2

.312" Transverse 1 .7 10.7 0.5 4.5 2.8 2.7

Longltudmal 3M) and the balance iron with residual impurities.

EXAMPLE #2 CMn P s Si Cu 01' Zr Al BTl Cb Ladle chemistry .17 .02 010 .024 .78 .03 .70 .00 .041 .0007 .03 Becheck chemistry 250 gauge .79 .04 .70 .08 .041 .0007 .03 .056 3125 gauge. .78 .04 .68 .07 .040 .0007 .03 .055

1 Added in mold.

MECHANICAL PROPERTIES 2. A low carbon, 75,000 p.s.1. minimum yield strength alloy steel conslsting essentially, by weight, of Brinnell Elonhardness YS TS gation, Bars number (p.s.i.) (p.s.i.) inches YP Bend n Percent As rolled 27 0 .250 gauge 223/241 81, 600 110,780 Carbon About .07 20.

31313333333: 33104533333: H3122) Manganese About 212 6 200 m2 080 Silicon About .50-1.0. 3125gauge" i 1 1 Chromium About .50-.30. 94,280 103,120 Zirconium About .05.20.

Boron About .0005.0025. Titanium About .15 max. HARPY V IMPACT TEST DATA Columbium About [FL-lbs. at temperature F.] 6 Phcsphorus R 2 4 Sulphur Max. .05. Thickness '1 32 0 0 0 Copper Max .35. .250" 7.0/4.7 5. 5 3.3 4.7/3.0 3.2/2.5 2.3 2.0 (LIT) Al i M ()7 .3125" --2s. 12.3 15. 0 7.5 3. 8/5.8 4.5 3.5 4.5 3.0

The process taught by the present invention, in addiand the balance iron. tion to or in combination with the chemistry, also contri- 3. A low carbon high tensile strength alloy steel suitbutes to the desirable characteristics obtained. In practice able for Welding and characterized by minimum tensile the alloy steel is provided in billet form, that is in a suit- 75 strength of 75,000 p.s.i. in the as rolled condition without subsequent heat treatment consisting essentially, by

weight, of

Percent, about Carbon .07.20 Manganese .75l.15 Silicon .50-1.0 Chromium .50.80 Zirconium .05.20 Boron .0005-.0025 Titanium about .15 max.

Columbium .01-.06

and the balance iron with residual impurities.

References Cited UNITED STATES PATENTS HYLAND BIZOT, Primary Examiner U.S. CI. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTTON Patent No. 3,689,258 Dated September 5 1972 In ent R.

It is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:

, Column 3, line 8, (Example #1) 518". should read 5 l/8" line 59, (Example #2) under the column "Bend", "1 l/Z X" should read 1 1/2 x t (Example #2) "CHARPY "V" IMPACT TEST DATA" should read as follows:

CIIARPY "V IMPACT TESTDATA [FL-lb. at temperature 1'-.]

Thickness Rll 32 0 -20 -40 .250 (.3J4X1J7X2J65).-. 7. 0/4. 7 5. 5/3. 3 4. 7.3. O 3. 2H,. 5 2. O (l l) .3125" (.3U4X295X2J65). 0/12. 3 15. 0/7. 6 8. 8/5. S 4. 5/3. 5 4, 3 15. 0

.(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting. Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM'DC 60376-5 69 U,S. GOVERNMENT PRINTING OFFICE: [969 0-366-334. 

